This invention relates to a process for treating soils to reduce the concentration of elemental mercury in soils. Elemental mercury is a common contaminant in soils near chlor-alkali facilities, mercury mining/retort sites, gold mining sites, natural gas pipeline transfer and processing stations, industrial facilities that produce mercury compounds, facilities that use (or have used) mercury manometers, and specialized operations such as the Y-12 Plant at Oak Ridge. To date, the most common strategy to address elemental mercury in soil is physical removal (digging up the soil) for offsite disposal or processing. Physical removal is costly at most sites and may not be feasible at many sites due to contamination depth or cultural interferences (buildings, utilities, roads, etc.). As a result, a variety of “in situ” techniques have been developed or proposed to address elemental mercury contamination in soils without the need for physical removal.
U.S. Pat. No. 7,692,058 describes a process to extract elemental mercury from soils in which heated tubes are used to create migration conditions for mercury in the soil which reacts with sulfur reagent sinks. The elemental mercury migrates to a column of sulfur and reacts to form a mercury sulfide compound. This technology requires using heat to establish an increased vapor phase concentration that will encourage mercury diffusion toward the sulfur sink, but this process does not effectively address residual mercury that may remain present throughout the soil as the site approaches cleanup.
U.S. Pat. No. 6,962,466 discloses a mercury vaporization system within soil using heat in conjunction with a vacuum system to increase vapor phase concentrations and remove mercury vapors in the produced soil gases. The technology described in the '466 patent does not address residual amounts of mercury that would remain throughout the soil as the site approaches cleanup.
U.S. Pat. No. 4,354,942 describes an “in situ” process for stabilizing soluble mercury using inorganic sulfur compounds. The process is used for land areas including landfills and low ground sediment deposits. The sulfur stabilizing compounds require physical mixing into upper soil layers and then relies upon rainfall or irrigation to introduce the sulfur agents to low ground. The stabilizing agent may also be introduced using high-pressure injectors or other injection methods or equipment commonly used in hydrology and petroleum technology.
U.S. Pat. No. 5,595,644 discloses a physical intermixing of mercury contaminants with the gaseous solution of sulfur trioxide. Elevated temperatures to increase the efficiency of the reaction are discussed but the technology is directed to some type of above ground reactor or processing of the materials and does not discuss an “in situ” process.
U.S. Pat. No. 8,025,160 discloses using sulfur-impregnated clays to function as a removal media for mercury compounds. The disclosure is directed towards using the reactive media in some type of above ground reactor and does not envision “in situ” treatment of soils.
There remains a need for a process of treating or stabilizing elemental mercury present in soils which is compatible with low levels of mercury that remain in soils following traditional mercury removal steps. Accordingly, there remains room for improvement and variation within the art.